156 COPE. [VoL. III. 
In the eared seals (Otariidz) the hind limbs are somewhat free 
from the body integument, so that they can be turned forward 
when on land. They are further enclosed in the true seals 
(Phocidz) so that their motion is very slight and they cannot 
be used for progression on land, and are available only for 
swimming.! It is supposed by Gray and Ryder that the solar 
and digital parts of the posterior limbs of the seals are repre- 
sented in the flukes of 
the Getacea,;.)” hese 
parts are supposed to 
have separated from 
the proximal parts of 
the limbs, which have 
been reduced in size; 
and finally nearly atro- 
phied through disuse. 
This view is supported 
by Ryder by consid- ~ 
erations derived from 
studies in the embry- 
ology and anatomy of 
the Ceétacea,?’ with 
much force. The phy- 
logeny, however, re- 
mains uncertain, owing 
to our extremely de- 
fective knowledge of 
the extinct ancestors 
of their order. 
Figure 6.— Muscles of the posterior leg of Pu- 
zorius vison, showing the position of the gluteus max- : 
imus (Gma.) muscle; Ge, gluteus medius; #, rec- The earliest aPPprox- 
tus; V, vastus. imation to the rela- 
tions of the muscles and bones of the hind legs of the seals 
is seen in the aquatic Mustelidz, as the otters and the mink. 
In the latter (Putortus vison) the gluteus maximus muscle has 
extended its insertion all the way to the distal extremity of the 
tibia, thus flexing that segment, and gaining power in the stroke 
1 On the Development of the Cetacea ; Report of Commissioner of Fisheries of U. 
S., 1885 (1887), p. 445. 
2 On the Eared Seals, Otartide, with Detailed Descriptions of the North Pacific 
Species. By J, A. Allen. Aull. Mus. Compar. Zoblogy, Cambridge, I1., No. 1. 
